.post表单数据到php

Question

我发送表格数据如下：

j.post('data_handler.php', {
        flag: 'signUp',
        username: username,
        password: password_register,
        birthDate: birthDate,
        firstname: firstname,
        lastname: lastname,
        email: email
    },

和data_handler.php获取信息：

case 'signUp': //flag

        // Get the user signup information
        $user = $_POST['username'];
        $firstName = $_POST['firstname'];
        $lastName = $_POST['lastname'];
        $birthDate = $_POST['birthDate'].'T23:30:58.000Z';
        $email = $_POST['email'];
        $password = $_POST['password'];

并传递给函数：

ValidateReg($user, $password, $firstName, $lastName, $email, $birthDate);

...由于某种原因，数据未通过，全部为空/空;我做错了什么，建议/帮助，谢谢！